Multistage crystallization process



K; H. HACHMUTH MULTISTAGE CRYSTALLIZATION PROCESS April 15, 1952 2 SHEETSSHEET 1 Filed July 11, 1949 INVENTOR KJLHACHMUTH BY N t 6 x PM A TTORNE YS April 15, 1952 K. H. HACHMUTH 2,593,300

MULTISTAGE CRYSTALLIZATION PROCESS 2 SHEETSSHEET 2 Filed July 11, 1949 FIG 2 IN VEN TOR.

KHHACHMUTH BY WWZELW @Me.@w

A 770/?NEYS Patented Apr. 15, 1952 MULTISTAGE CRYSTALLIZATION PROCESS Karl H. Hachmuth, Bartlesville, 0kla., assignor to Phillips Petroleum :Company, a corporation of Delaware Application July 11,1949, Serial No. 104,048

6 Claims. (Cl. 250-666) This invention relates to the separation of mixtures of compounds by crystallization. In one'of its more specific aspects, it relates to the multi-' stagecrystallization of mixtures of compounds.

In another specific aspect, it relates to the sepa ration of solid solution-forming mixtures into their components. In another specific aspect, it relates tolthe purification of compounds by crystallization. In still another specific aspect, it relates to an apparatus for carrying out such separations.

' When crystals are frozen from a mother liquor comprising a mixture of compounds which do not form solid solutions, it is theoretically possible to attain pure material by a single crystallization. Actually, the crystals separating from partially frozen mixtures usually give a melt that is far from pure. This is particularly true in the case of hydrocarbons or other organic compounds, and is due tothe entrapment of mother liquor by the fine, oftenfibrous crystals. This mother liquor is held tenaciously and is not easily separated;

Pressingvacuum filtration or centrifuging may remove a portion.

When the components of a mixture form solid solutions, it is not possible either theoretically or actually to obtain a pure material by one crystallization. In such cases, the crystals separating from such a mixture do not have the same composition as the mother liquor. The material crystallized is a mixture of the components present, the ratio depending on the composition of the starting material and on the equilibrium characteristics for: the particular system. Thecrystals will be richer with respect to the highermelting component of the mixture than the liquid from which those crystals were solidified. A

eutectic is considered as being the lower-melting.

component.

If equilibrium between the crystals separated from a mixture of solid solution-forming components and the remaining liquid could be easily attained. then separation of the components could be obtained by moving the crystals countercurrently to a liquid which becomes increasingly richer with respect to that component tending to be preferentially removed by freezing. The crystals could be melted and a portion of the melt' returned countercurrently to the moving crystals while the remainder of the melt would be removed as product. At the opposite end of such a crystal lizer, cooling could be applied to generate the crystals. The unfrozen liquid would be removed as the pure, less-easily frozen fraction of the orig inal mixture. The crystals formed would always,-

sible, its efficiency is disappointingly low, because of the time required for the solid liquid to reach equilibrium.

Resort to alternate partial or complete melting and freezing is usually the result of attempts'to obtain pure products by countercurrent continuous crystallization. In such a process, the energy requirements and amount of heat transfer required are inordinately large because the heat of crystallization must be added and removed many times throughout the process.

I have discovered a method by which it is possible to obtain the advantages of alternate melting and freezing without the disadvantages of using large heat exchange surfaces and heat transfers during the process.

The principal object of my invention is to provide a means of separating mixtures of compounds by crystallization. Another object is to provide a method of removing the excess saturating component from a eutectic-forming mixture. v I

Still another object is to provide a method of separating solid solutions into their'components.

Still another object is to provide an apparatus for the efficient separation of mixtures intotheir components'by crystallization methods I Other objects and advantages of the inventi'onii will be apparent from the following description;

drawingsand disclosure.

In the drawings:

Figure 1 is a part cross-sectional, part deni tional view showing my apparatus.

Figure 2 is a transverse cross-sectional viewer:

the crystallization chamber taken along the pla 2--"-2 of Figure 3. I Figure 3 is a portion of a" longitudinal:cros

sectional view of the crystallization chamber":

taken along plane 3--3 of Figure 2. In Figure 1, an inclined crystallizationchamber 6 is shown positioned above a similar chamber 1.

A feed mixture enters th system through'lines 8 and 9. Line 9 enters crystallization chamber 6 at transverse trough i I. The lower portion of the inclined crystallization chamber is divided into segments by a series of transverse battles [2. R0-

tatably and coaxially mounted within said crystal-' lization chamber 6 is a smaller cylinder I3. r A

plurality of scraper paddles 14 extend radially outward from rotatable cylinder [3 and corre spond to the troughs formed by said transverse baffles so *thatwhen the smaller cylinder is" retated, the paddles scrape the bottoms of the re- 2 1 be moved towards the warmer end of the crystal: lizer. While such a process is'theoretically'posa and remaining large spective troughs. Motor it rotates cylinder l3 by .means of gears l1 and I8. Product take off line [9 leads from the last compartment on the low .end of crystallization chamber 5 for removing the lower-melting fraction produced by the separation.

Surrounding the bottom portion of the inclined crystallization chamber 6 is a cooling jacket 20. This jacket is divided internally into compart- -ments by a series of baffles 2| having openings 22 therethrough.

The feed mixture, as it enters compartment H of the crystallization chamber 6, is partially cooled by the abstraction of heat by means of refrigerant flowing through cooling jacket 20 so that at least a portion of the mixture is crystallized. The crystallized material is scraped from the trough by means of the corresponding ro-' tating paddle. As the frozen material is transported towards the top of the crystallization chamber by the continued rotation of cylinder, said crystallizedmaterial falls over the inner edge of the paddle onto rotatable cylinder [3, which is maintained at a temperature sufiiciently high to melt the frozen material. The melted material flows from longitudinal trough 123 at its open end, whichis towards the higher end of the cr stallization chamber 6 and falls into the transverse trough next adjacent on the high side of the trough from which it was removed. The uncrystallized material displaced by the addition of the melt to a transverse trough overflows the bafile on the low side of said trough into the next adjacent trough on the low side. The last transverse trough or compartment 24 on the high end of crystallization chamber 6 does not have a paddle for scraping solid material and is not cooled by the jacket since it is contemplated that all material entering said compartment 24 will leave the crystallization chamber through outlet line 26 which leads to the lower portion of the jacketed compartment of a similar crystallization chamber l'. The product outlet line 21 from the low side of crystallization chamber 1 leads to pump 28 and thence into ,line 9 which leads to chamber 6 as previously described. Crystallization chamber 1 has a cooling jacket 29 surrounding a lower portion. Product outlet line 3|, leading from the last compartment on the high end of chamber 1. is the outlet line for the higher-melting fraction produced by the separation and leads to an external storage, not shown.

The refrigerant or heat transfer liquid moves through the apparatus in a closed system. Beginning with line 32, the refrigerant liquid flows therethrou-gh into cooling jacket 20 of crystallization chamber 6 at the low end of said chamber. The refrigerant leaves jacket 20 through line .33 and valve 34 and enters jacket 29 of crystalllZation chamber 1 via line 36. Refrigerant outlet line 31 from jacket 29 leads to pump 38, thence into separator 39 via line 40.

The gaseous refrigerant which results from the evaporation of the liquid refrigerant in jackets 20 .and v29 leaves via lines 42 and 43, respectively, which join to form line 44. Refrigerant compressor 4B is interposed in line 44 ahead of'cooler 41. Cooler 4! has an outlet line 48 which leads to a second separator 49. The liquid refrigerant leaves the bottom of said second separator .49

via lines M and 40 which lead to the previously,

described separator 39. The uncondensed 'refrigerant leaves an upper portion of separator 49 through line 5! and at least a portion enters 7 ing fractions.

rotatable cylinder 52 of crystallization chamber 1. The gaseous portion of the refrigerant from separator 39 leaves an upper portion of said separator via line 53 which leads to rotatable cylinder l3 of crystallization chamber 6. As desired, a portion of the gaseous refrigerant leaving separator 49 through line may be passed into line 53 via line 54 controlled by valve 56 or via line 5! into central cylinder 52. The liquefied refrigerant leaving rotatable cylinder [3 at its low end is passed through line 51 to cooling jacket 20 via line 32 or, as desired, a portion may be caused to flow through line 58, line 59 and line 36 into jacket 29. .The liquefied and gaseous refrigerant from rotatable cylinder 52 of crystallization chamber 1 leaves said cylinder via line 6| which leads to separator 39. The liquid refrigerant leaves the lower portion of said separator 39 via line 62 and as desired may flow through line 59 to ultimately reach jacket 29 or through line 58 into jacket 20 via line 32. .Sealing glands 63 are provided in the lines joining the rotatable cylinders.

.In .Figure 2, the crystallization chamber 6 is shown as having on its under side a cooling jacket Zflhaving vbaflle 21 with openings 22 therethrough.

Paddle l4 scrapes through the transverse trough formed by transverse bafiles l2. Each of the rotating paddles has a corresponding melting trough 23 which extends longitudinally along rotatable cylinder [3 for a distance less than twice the width of the transverse troughs. .Longitudinal trough 23 is closed on the end towards the low side of the crystallization chamber and is open at the end towards the high side of the crystallization chamber. At least one of the walls 66 of said trough 23 follows aspiral course along the rotatable cylinder so that liquid in said trough will flow towards the high side of the crystallization chamber. This is necessary be cause the apparatus is inclined upward towards the open end of said longitudinal troughs 23. Drip guide 61, which is a disc surrounding the rotatable cylinder 13 at a point just short of the end of trough 23 prevents liquid from flowing along rotatable cylinder l3 toward the lower end of the apparatus.

In Figure 3, the longitudinal troughs 23 along rotatable cylinder I3 are more clearly shown. Each trough has an end closure 68 at the lower end and is open at theopposite end. The position of drip guide .61 is more clearly shown in this figure. The liquid formed by melting solid material which has been scooped from transverse compartment II by scraper l4 pours from trough .23 .into the high side of the next adjacent transverse compartment towards the higher .end of the apparatus. In the drawings, thisjis the next trough to the right.

Operation My apparatus and process are particularly efficient in the separation of binary mixtures of compounds into higher-melting and 1ower-melt The higher-melting fraction is either "the higher-melting component or the saturating component in substantially pure form. With solid solution-forming mixtures that do not form eutectics, the lower-melting fraction is the lower-melting component in substantially pure form and complete separation can be made by crystallization. In the case of eutectic-forming mixtures, the higher-melting fraction is the saturating component of the mixture in substantially pure form while the lower-melting fraction is substantially pure eutectic. Sometimes;'s'olid so tillation, solvent extraction, chemicalmean s, .or

other applicable means. I can also separate mixtures containing more than two components; However, each unit can separate the mixture into only twofractions. Those fractions which contain more than one component may be-separated in another unit or stored and passed through the original unit after the first separa-' tion is complete. l

The operation will be more clearly understood from the following description of a separation. The feed material which is to be separated into two fractions enters the upper crystallization chamber near the warmer end of said chamber. In the drawing, I have shown the feed as entering the second transverse trough from the warmer end. This feed is cooled by the refrigerant circulating through the jacket surrounding the lower portion of said chamber so that a portion of the feed mixture is frozen or crystallized on the vessel wall. The scrapers l4 rotating with the central cylinder [3, periodically passes through this trough and scrape the accumulated crystals from the stationary cylinder wall. On continued rotation of the central cylinder, the crystals on the scrapers are elevated until they slide off the scrapers onto the central cylinder. The trough on said central cylinder surrounding the base of each scraper retains the material that falls from said scraper. This material is melted by contact with the relatively warm central cylinder and the melt flows through said trough towards the warmer end of the crystallization chamber and pours into the-transverse trough next'adjacent towards the warmer end of the apparatus. The melted material is added to the transverse trough at a point near the high side of said trough to permit thorough mixing of the melt with the contents of said transverse trough. The addition-ofthe melt displaces an equivalent volume of the liquid already present in the trough. Since the-crystallization chamber is inclined upward from the cooler end, the dis placed liquid in each trough always flows toward the cooler end of the apparatus. When the liquid reaches the cooler end of thefapparatus, the separation is substantially complete and the lower-melting fraction is'removed from the cooler end of the crystallization chamber; Eventually, the higher-melting material reaches the last transverse trough on the warmer end of "the:

apparatus and is removedtheref-rom.

The highermelting fraction fro'm'- the"iirst crystallization chamber istransferred to a second similar crystallization chamber 'and is introduced at a point near the cooler end 'of-said' second chamber. Material 'Which" crystallizes from this material as it enters the second chamber is removed from contact with the liquid and is remelted by contact with the relatively warm central cylinder. The melt from each ,por-

tion of the crystallized material is'rnoved to the next adjacent transverse trough "on the warmer. Eventually, a port'ionof the original "feed' side. mixture reaches the warmer'end of said second pure form freeze.

tion-forming mixture, the higher-melting fraction will be the higher-melting component. If the feed mixture is a eutectic-forming mixture, the higher melting fraction will be the saturating component of said mixture.

The temperature at the cooler end of the apparatus must be close enough to the melting point of the lower-melting'fraction to be removed so that said fraction will be completely liquid if it contains less than a predetermined amount of the higher-melting fraction. If more than said amount is present, a portion should The temperature at the warmer end should be about the melting point of the highermelting fraction.

In each transverse trough of each chamber, with the exception of the end trouglnthe action is the same. The liquid therein is cooled to crystallize a portion of the crystallizable. material. This crystallized material is then removed from contact with the liquid and is transferred toward the warmer end of the apparatus, thereby displacing an equal volume of the remain-,

ing liquid towards the cooler end of the apparatus.

My apparatus, with the series of transverse troughs, provides a means for maintaining a composition gradient throughout the system. Melting and recrystallization occurs in each of i said troughs and the liquid added to each trough is always richer with respect to the higher-melting fraction than the liquid which it displaces.

Without a positive means for maintaining separate portions of the liquid throughout the systerm, it is almost impossible to maintain a composition gradient, since liquids in contact with each other are easily mixed by a small amount of agitation. While I have shown two separation crystallization chambers, I can use only one such chamber. The use of a single chamber apparatus would simplify the construction but the proper temperature and enthalpy relationships would be more difficult to maintain in a single chamber apparatus. A two chamber apparatus is the preferred modification of my invention.

In order to provide the proper cooling and heating for efficient operation, a mixed refrigerant is preferred. This is a refrigerant consist-,

ing-of two or more compounds which have different volatilities. Such a mixed refrigerant will evaporate over a temperature range and furnish refrigeration at different temperature levels without the use of complicated equipment. Conversely condensation of such a mixed refrigerant furnishes heat at difierenttemperature levels.

It is evident that I wish to remove heat over a considerable temperature range and to simultaneously supply heat over another temperature range. For best operation, the amount of heat removed in each transverse trough (except for the terminal troughs) should be very nearly the same. The amount of heat supplied to :melt the crystals from each scraper should be approximately the same as that removed in each corresponding trough. This means that the tempera ture difference between the central tube and the outer cylinder must be rather constant throughout the, equipment. This condition can be apant flows to the right through the jacket continually rising in temperature as it is boiled away in refrigerating the stationary cylinder. Any liquid refrigerant remaining at the right end of the jacket is removed through conduit 33, receives additional refrigerant through line 59 if needed, and passes by conduit 35 to the left hand end'of the refrigerated jacket 29 of the lower chamber. The refrigerant passes to the right through this jacket continually rising in temperature as it is boiled away. Any unvaporized refrigerant is removed through conduit 31 and A pumped through conduit 40 into the lower separator 39.

The vapors evolved in the refrigerated jackets 2B and 29 are collected by conduits 42 and 43 and passed through conduit 44 to a compressor 46 where :the pressure is increased to the level required by the heating tubes. The compressor discharges to a cooler 41 where the vapor is cooled and may be partly condensed. The cooled fluid flows through conduit 48 to a separator 49 where the liquid is separated and removed through conduit 4| thence passing through conduit 40 to the lower separator. Vapor leaving the upper separator 49 passes through conduits 50 and 5| into the central heater tube of the lower vessel. Here the vapor is partly condensed as it passes down the tube, and drops in temperature as it is condensed. The mixed vapor and liquid passes through conduit 6| to the lower separator where the residual vapor i removed through conduit "53. This residual vapor plus additional vapor from conduit 54, if needed, passes to the heating tube l3 in the upper vessel. Here it is completely or partially condensed and dropsin temperature as it condenses. The resultant condensate and residual vapor (a separator might, if desired, be provided at this point to separate the residual vapor) leaves the tube by conduit 51 and all or part enters conduit 32 thereby completing the circuit. Conduit 58 serves to remove unwanted refrigerant or add more refrigerant to32 if needed.

By a proper choice of refrigerating mixtures and pressure levels for various parts of the equipment, almost any conceivable regular temperature enthalpy relationship can be obtained. A relatively non-volatile liquid may be used in the mixture so that some residual liquid always remains. This would cause a large temperature rise at the hot end of the refrigerating jackets with little heat transfer. Inclusion of a relatively non-condensible vapor would give large temperature drops at the cold end with little heat transfer. Inclusion of two components forming non-ideal solutions will give fiat temperature curves in the middle of the apparatus. Inclusion of immiscible compounds will give other special effects. The variations obtainable are almost without limit and the specific requirements will determine the refrigerant makeup. However, it is well within the skill of any good engineer to determine the specific requirements.

The central heating tubes can be equipped with spiralelevating screws in their interior so that the condensate can be removed at their upper ends, thereby obtaining another type of temperature curve and, in case the vapor is completely condensed, eliminating the necessity of one or two packing glands. Even if the vapor is not completely condensed, provision of a central eduction tube will permit elimination of the lower packing glands.

At the loss of some flexibility, the upper and lower vessels can be joined end to end :for forming a single unit. Piping would be greatly simplified but it would be more difficult to obtain proper temperature enthalpy relationships.

This equipment is very efficient energy-wise because it is necessary to pump heat only between the cooling and heating levels, not from the cooling level to cooling water temperatures. At low temperatures, heat exchange between the stream :in conduit 44 and stream 48 or its equivalent should .be provided. Also, the feed in all cases should be cooled by an auxiliary cooler to operating temperature before entering the equipment. The liquid feed should be cooled to the temperature jus't'above that at which the first solid begins to form.

Instead of adding the melted material :back to the next adjacent transverse trough on the warmer side, it may be :added back to the second or even -third trough. In such a case, the troughs and paddles on the central rotatable cylinder would be spaced at or'9 0 intervals and the troughs would be extended a distance slightly less than three or less than four transverse troughs.

The last transverse baffle on the warm end of the crystallization chambers is lower than the other baiiies so that liquid overflows into the last trough on the warm side -from the next lower trough. This prevents freezing in the outlet trough.

It is evident that my .invention is useful in the separation of mixtures of compounds which These mixor any particular mixture of refrigerating liquids but is limited only by the following claims.

Having described my invention, I claim: 1. The process for separating crystallizable material from a liquid mixture which comprises the steps of maintaining a plurality of serially disposed adjacent bodies of said mixture, maintaining a temperature differential between the ends of said series of bodies, abstracting heat from said mixture to freeze a portion of the crystallizable material along the length of said plurality of serially disposed bodies, removing said frozen material as discrete portions from contact with the remaining liquid, melting the portions of said frozen material and returning the melt of each to said liquid at a point nearer the warmer end of said serially disposed liquid bodies than the point at which it was removed, removing a stream of liquid comprising a lowermelting fraction from the cooler end of said series of bodies, and removing a second stream of liquid comprising a higher-melting fraction from thewarmer end of said series of bodies.

2. The method of separating amixture of compounds into a higher-melting fraction and a lower-melting fraction which comprises the steps of maintaining a plurality of serially disposed adjacent liquid bodies of the mixture, maintaining a relatively low temperature at one end of said series of bodies and a relatively high temaseasoo perature at the other end of said series of bodies, cooling a peripheral portion of said serially disposed liquid bodies to freeze a portion of the mixture, removing the frozen material as discrete portions from contact with the liquid, melting the solid portions so removed and returning the melt of each to the serially disposed liquid bodies at a point nearer the warmer end of said series of bodies than that from which it was removed, removing a liquid comprising higher-melting fraction from the warmer end of said series of bodies, and removing a liquid comprising a lowermelting fraction from the cooler end of said series of liquid bodies.

3. The method of separating a mixture of compounds which melts over a range of temperatures into a higher-melting fraction and a lower-melting fraction which comprises the steps of maintaining a plurality of serially disposed and inclined adjacent bodies of the mixture, maintaining a relatively low temperature at one end of said series of inclined bodies, said low temperature being above the melting point of the lowermelting fraction but below the melting point of the higher-melting fraction, maintaining a relatively high temperature at the other end of said series of inclined bodies, said high temperature being above the melting point of said highermelting fraction, maintaining intermediate temperatures intermediate said ends, continuously abstracting heat from said series of inclined bodies along a substantial portion of their length to freeze a portion of the crystallizable material, removing said frozen material in separate portions from contact with the liquid, melting each portion of the frozen material out of contact with the liquid and returning the melt to said serially disposed and inclined liquid bodies at a point nearer the warmer end than that from which it was removed, removing a stream of liquid as a lower-melting fraction from the relatively cool end of said series of inclined bodies, and removing a stream of liquid as a higher-melting fraction from the relatively warm end of said series of inclined bodies.

4. The method of separating the components of a binary, solid solution-forming mixture of organic compounds which comprises the steps of maintaining a plurality of serially disposed and inclined adjacent bodies of the mixture, maintaining a temperature differential between the ends of said series of inclined bodies, abstracting heat from the peripheral portion of said serially disposed and inclined liquid bodies to freeze a portion of the material in each of said adjacent bodies, periodically removing the crystallized material from each of said adjacent bodies, melting said material and returning the melt to the next adjacent body on the warmer side, thereby displacing an equal volume of liquid and causing said displaced liquid to flow to the next adjacent body on the cooler side, removing one stream of liquid from the cooler end of said series of inclined bodies and another stream from the warmer end, and adding a stream of fresh feed mixture to said serially disposed and inclined liquid bodies at a point intermediate the ends.

5. The process for separating crystallizable material from a liquid mixture which comprises the steps of maintaining a plurality of serially disposed adjacent bodies of said mixture, maintaining a temperature differential between the ends of said series of bodies by means of a refrigerant consisting of at least two compounds which have difierent volatilities, abstracting heat from said mixture to freeze a portion of the crystallizable material along the length of said plurality of serially disposed bodies, removing said frozen material as discrete portions from contact with the remaining liquid, melting the portions of said frozen material and returning the melt of each to said liquid at a point nearer the warmer end of said serially disposed liquid bodies than the point at which it was removed, removing a stream of liquid comprising a lowermelting fraction from the cooler end of said series of bodies, and removing a second stream of liquid comprising a higher-melting fraction from the warmer end of said series of bodies.

6. The method of separating the components of a binary, solid solution-forming mixture of organic compounds which comprises the steps of maintaining a plurality of serially disposed and inclined adjacent bodies of the mixture, maintaining a temperature differential between the ends of said series of inclined bodies, abstracting heat from the peripheral portion of said serially disposed and inclined liquid bodies to freeze a portion of the material in each of said adjacent bodies by means of a refrigerant consisting of at least two compounds which have different volatilities, periodically removing the crystallized material from each of said adjacent bodies, melting said material and returning the melt to the next adjacent body on the warmer side, thereby displacing an equal volume of liquid and causing said displaced liquid to flow to the next adjacent body on the cooler side, removing one stream of liquid from the cooler end of said series of inclined bodies and another stream from the warmer end, and adding a stream of fresh feed mixture to said serially disposed and inclined liquid bodies at a point intermediate the ends.

KARL HACHMUTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,906,534 Burke May 2, 1933 1,951,923 Cartoux Mar. 20, 1934 2,147,222 Treub Feb. 14, 1939 2,164,769 Govers July 4, 1939 2,354,895 Ward Aug. 1, 1944 2,427,042 Bowman Sept. 9, 1947 2,480,242 Hirschler et al Aug. 30, 1949 2,486,014 Evans Oct. 25, 1949 2,493,567 Birch et a1 Jan. 3, 1950 

1. THE PROCESS FOR SEPARATING CRYSTALLIZABLE MATERIAL FROM A LIQUID MIXTURE WHICH COMPRISES THE STEPS OF MAINTAINING A PLURALITY OF SERIALLY DISPOSED ADJACENT BODIES OF SAID MIXTURE, MAINTAINING A TEMPERATURE DIFFERENTIAL BETWEEN THE ENDS OF SAID SERIES OF BODIES, ABSTRACTING HEAT FROM SAID MIXTURE TO FREEZE A PORTION OF THE CRYSTALLIZABLE MATERIAL ALONG THE LENGTH OF SAID PLURALITY OF SERIALLY DISPOSED BODIES, REMOVING SAID FROZEN MATERIAL AS DISCRETE PORTIONS FROM CONTACT WITH THE REMAINING LIQUID, MELTING THE PORTIONS OF SAID FROZEN MATERIAL AND RETURNING THE MELT OF EACH OF SAID LIQUID AT A POINT NEARER THE WARMER END OF SAID SERIALLY DISPOSED LIQUID BODIES THAN THE POINT AT WHICH IT WAS REMOVED, REMOVING A STREAM OF LIQUID COMPRISING A LOWERMELTING FRACTION FROM THE COOLER END OF SAID SERIES OF BODIES, AND REMOVING A SECOND STREAM OF LIQUID COMPRISING A HIGHER-MELTING FRACTION FROM THE WARMER END OF SAID SERIES OF BODIES. 